Transfer Line Exchanger Gasket

During the production of hydrocarbon compounds, the heat resistant gaskets coated with graphite on the transfer line exchanger (TLE) had degraded. While in service, the TLE was subjected to cracked gas at a temperature and pressure of 850 ºC and 1.5 ksc, respectively. Major maintenance of gaskets are usually carried out every 3 years. However, leakage of ethylene gas was detected during the latest inspection 3 months ago. This event led to furnace shutdown and productivity loss of ethylene about 30 million baht per day.

After conducting failure investigation, the results revealed that the degradation of gaskets might occur from the over tightening torque during installation. The 200,000 baht inspection was carried out on the remaining gaskets. As a result, 24 gaskets from 12 production lines which were installed in the same period with the degraded ones were also replaced to prevent catastrophic damage in the future.

The results from this project include:

The methodology to prevention the reoccurrence of this failure by applying the proper tightening torque.

Saving the replacement cost of gasket from every 3 months to every 3 years which would cost about 8.8 million baht.

Hydrocarbon Transfer Coil

Cracking furnace coil in one of the petrochemical plant had experienced swelling. The coil was used in ethylene furnace for transferring Naphtha/HC gas at a temperature of 875 ºC. The outer wall was subjected to flue gas at 900 ºC. The coil was made of heat resistant alloys (25Cr35NiNb) through centrifugal casting process. Hydrocarbon gas leaked during operation. Moreover, the swelling of coil in the other cracking furnace has increased over time. Therefore, the cause of swelling must be investigated and evaluated to confirm that the failure is in acceptable criteria. The results were also used for improvement the procedures for safety operation. After conducting failure investigation, the results revealed that the decoking process caused the reduction of coil thickness and the formation of degraded layer on the coil surface. This project suggested that the swelled coil must be replaced immediately due to the presence of micro-cracks that might cause crack propagation. After receiving the analytical data, the plant decided to modify the decoking process and replaced the swelled coil one by one in the cracking furnace.